Handle standard name or units set to None when creating GriddedData.
Related to Trac #576 and #374 - more changes for colocation where data and sample points are on different longitude ranges.
Related to Trac #576 and #374 - following on from commit 564f2f6019 - more changes for colocation where data and sample points are on different longitude ranges.
Merge branch 'devel' of proj.badc.rl.ac.uk:jasmin_cis into devel